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Re: [Paparazzi-devel] Switching Regulator

From: Gareth Roberts
Subject: Re: [Paparazzi-devel] Switching Regulator
Date: Thu, 03 Mar 2011 14:52:33 -0000
User-agent: Opera Mail/11.01 (Linux)

Hi Micheal,

I only experienced issues when driving 4 full size servos (all concurrently).
Funjets and friends which use 9 gram micro servos are fine.
The max draw of a HS-55 micro servo is about 0.4A while translating or jammed (we had some hooked up to a current sensor last week). A full size servo was hitting almost 0.9A which translating, although jam current was much lower.

You could quite easily calculate the quiescent draw by connecting a 5V lab supply to one of the paparazzi 5V outputs. That + modem @ transmission + max servos must be less than the 2.25A (although 2A to keep it safe). Be aware that anything on the 3.3V bus (which is definitely not recommended for external use) will increase the load on the 5V regulator.

Regarding regulators, if you are using an ESC, purchase one with a BEC. Typically this will give you around 3A of 5V for almost no additional weight. Otherwise standalone BECs are available for RC aircraft with IC engines - these are widely available, robust and dead easy to use.

Or you can just use a few LM7805 and wire them up yourself - they aren't the most efficient things, but they are cheap, light and simple.

Hope this helps,

n Thu, 03 Mar 2011 14:23:48 -0000, Michael Weigand <address@hidden> wrote:

Paparazzi Community,

The TI switching regulator found on the Tiny architecture has a maximum
rated current draw of 2.25 A, and the wiki says that you can power external devices and sensors requiring 5v through it. However I have seen posts which do not recommend placing additional external loads on the regulator. What is
the safety margin for powering devices through the regulator? If you were
required to power a number of loads externally with a draw of 0.8-1.2 A what
small, lightweight regulators would you suggest?

Thank you for your feedback!


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